Last week, the Scandinavian nation announced it would use Lindholm Island to house criminals whose sentence of deportation cannot be carried out because they risk torture or execution in their home country.

Ms Bachelet expressed concerns about the plan on Wednesday, saying it is "very likely" to cause harm.

Lindholm Island in Denmark.

Reuters

"We have seen the negative impact of such policies of isolation and should not replicate these policies," the former Chilean president said.

"Depriving [these people] of their liberty, isolating them and stigmatising them will only increase their vulnerability.

"Sometimes there are difficulties encountered in returning migrants to their countries of origin when they're not accepted as refugees. But this should be addressed in a safe and humane way."

UN High Commissioner for Human Rights Michelle Bachelet on Wednesday.

AAP

Ms Bachelet also voiced concern around the language used in Denmark's immigration debate, after Immigration Minister Inger Stojberg labelled these individuals "unwanted".

'NO reason to be in Denmark'

The new arrangement was part of an agreement between Denmark's conservative coalition government and anti-immigration party the Danish People's Party (DF).

On Friday, Finance Minister Kristian Jensen said "there will be a ferry service to and from the island, but the ferry will not operate around the clock, and they must stay at the departure centre at night".